She was said to have carried out the attack after discovering her 18-year-old victim had started dating a former boyfriend.

Miss Young, who was 17 at the time and a senior pupil at Knox Academy, Haddington, suffered burns to her legs and permanent scarring when she took the viola down from a shelf and the acid poured out of the case.

Bowen, whose father is a QC, was jailed at Edinburgh Sheriff Court this week for 21 months for the “utterly wicked” incident.

The court had previously heard how the girls were both talented musicians, with Bowen playing the clarinet and Miss Young the viola in the school orchestra.

Molly Young suffered serious burns

When she pleaded guilty during a hearing on June 26, the court heard that that the 18-year-old wrote the fake letter to herself and signed it with her victim’s name.

Aidan Higgins, prosecuting, said: “On November 10 last year Emily Bowen prepared a letter which appeared to come from Molly Young in which she talked of Emily Bowen to kill herself. Subsequently Emily Bowen admitted it was she who was the author of the letter.”

Sheriff Michael O’Grady referred to the letter during his sentencing on Monday, saying Bowen’s “careful and premeditated actions” in September 2016, combined with the penning of the note, cast a “very disturbing light” on her thinking.

A friend, who did not want to identified, said: “Some folk in the town had sympathy for her after the acid incident as they thought it was a spur of the moment thing, but after finding out about the letter they soon changed their minds.”

Bowen’s father is Andrew Bowen QC, and a friend of the family said the teenager wanted to follow in his footsteps and was due to study law at Aberdeen University.

Knox Academy in Haddington

The friend added: “She is a very intelligent girl and she would have sailed through any degree she wanted to do.

“She has always looked up to her father Andy and I think it was a dream of hers to follow him in his profession.

“I do feel sorry for her in a way as she had everything in front of her, she has a great family and didn't ask for anything but you really cannot excuse what she did.”

Mr Bowen sat beside his daughter in the dock when she pleaded guilty to recklessly and culpably pouring sulphuric acid into Molly Young’s viola case during the court hearing in June.